Exhaust systems may include one or more particulate matter sensors to determine an amount of particulate matter (e.g., carbon contaminants such as soot) in an exhaust gas stream. In some examples, the particulate matter sensors may be resistive sensors with an exposed electrode on which the exhaust system particulate matter accumulates. The accumulated particle matter, gathered in sufficient quantity, causes a change in resistance. This change in resistance is used along with other powertrain operating parameters to infer a particulate matter leakage rate of the particulate filter. This leakage rate is compared to the allowable leakage rate of the powertrain system and is used to determine the health of the particulate filter. While this sensor is intended to measure small particle carbon based contaminants, other contaminants (e.g., non-carbon contaminants), such as oil additives, fuel contaminants, and residual materials from the exhaust system (e.g., iron oxide, etc.) may accumulate on the electrode. This contamination, if progressed sufficiently, results in decreased accuracy of the sensor and degrades an ability of the sensor to measure particulate matter leakage.
The inventor herein has recognized the possibility of excessive contaminant accumulation on the particulate sensor and a need for methods of protection from this contaminant exposure. A method is provided to allow for proper measurement of the particulate matter sensor while increasing the robustness of the sensor to normal contamination expected in the exhaust system. In the simplest implementation, the particulate matter sensor has three phases of operation: the first mode is a startup condition where the sensor is placed in an operational condition that limits the ability of liquid droplets to form on or damage the sensor ceramic substrate; the second mode is a normal measurement mode where the sensor performs and completes a normal measurement; and the third mode is a reduced contamination mode that allows for the sensor to be placed in an operational condition where the sensing element is put into a mode where potential contaminants are repelled from the sensing surface.
In one particular example, a method for a particulate matter sensor comprises generating an indication of particulate flow rate through a particulate filter based on particulate accumulation on a sensing element of the sensor. The method further comprises diagnosing the sensor based on the flow rate. The method further comprises, after diagnosing of the sensor is completed, heating a sensing element of the sensor to repel particulate from the sensing element. Thus, in one example, the sensor may diagnose the particulate filter during a measurement mode of operation. Further, the sensor may be heated to repel particulate, such as contaminants, during a reduced contamination mode of operation. The measurement mode and reduced contamination mode may be carried out at different times, for example. In this manner, while the sensor is not being used to generate information about the particulate filter, the sensor may be protected from accumulation of contaminants which may degrade performance of the sensor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.